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CVS HISTOLOGY
Dr. Nabil Khouri
http://anatomy.kmu.edu.tw/BlockHis/Block3/slides/block4_24.html
The Heart Wall
Cardiac Muscle • Contract as a single unit
• Simultaneous contraction
due to depolarizing at the
same time
• Intercalated disk to speed
depolarization automaticity
M -myocardium;
E - endocardium;
En -endothelium;
S -ubendothelial
layer
Cardiac Muscle Longitudinal Section
• Cardiac muscle consists of muscle cells mononucleated with centrally placed nucleus. Nuclei are oval, rather pale and which is 10 - 15 µm wide.
• Cardiac muscle is innervated by the autonomic nervous system.
• Cardiac muscle exhibits cross-striations.
• Cardiac muscle is for these reasons also called involuntary striated muscle.
X40 Magnification
cell nucleus
Intercalated Discs
One cell
The Cardiac
Muscle Cells
Adherens Junction Desmosome Gap junction
Fascia adherens – major portion
of transverse component.
Anchoring sites for actin, and
connect to the closest sarcomere.
Macula adherens –
(desmosomes) transverse and
lateral components. Bind
individual myocytes to one
another. stop separation during
contraction by binding
intermediate filaments, joining
the cells together. Macula
adherens junctions are also
called desmosomes.
Gap junctions - lateral
component. Allow action
potentials to spread between
cardiac cells by passage of ions
between cells, producing
depolarization of the heart
muscle. Allows muscle to act as
syncytium.
– Cardiac cells are connected by intercalated discs
– Intercalated discs house desmosomes and gap junction.
• Desmosomes provide strength so that the cell do not get ripped
apart during contraction
• Gap junctions are made of the connexin proteins and form a pore
through which the cells can communicate.
Cardiac Muscle Tissue
Cardiac Muscle “Cross section”
X40 Magnification
• The fibrous skeleton of the heart consists of masses of dense connective tissue in the
endocardium which anchors the valves and surrounds the two atrioventricular canals,
maintaining their proper shape. Section through a leaflet of the left atrioventricular
valve (arrows) shows that valves are largely dense connective tissue (C) covered with a
thin layer of endothelium. The collagen-rich connective tissue of the valves is stained
pale green here and is continuous with the fibrous ring of connective tissue at the base of
the valves, which fills the endocardium (En) of this area between the atrium (A) and
ventricle (V). The chordae tendinae (CT), small strands of connective tissue which bind
distal parts of valve leaflets, can also be seen here. The interwoven nature of the cardiac
muscle fibers, with many small fascicles, in the myocardium (M) is also shown.
Purkinje fibers 40X
Are modified cardiac muscle cells.
Compared to ordinary cardiac muscle
thicker cells: Contain large amounts of
glycogen fewer myofibrils.
Blood Vessels histology
• Blood is carried in a closed system of vessels that begins
and ends at the heart
• The three major types of vessels are arteries, capillaries, and
veins
• Arteries carry blood away from the heart, veins carry blood
toward the heart
• Capillaries contact tissue cells and directly serve cellular
needs
General Structure of Blood Vessels
Structure of blood vessel (Tunics)
• Tunica interna (tunica intima)
– Endothelial layer that lines the lumen of all vessels
– In vessels larger than 1 mm, a subendothelial connective tissue basement membrane is present
• Tunica media
– Smooth muscle and elastic fiber layer, regulated by sympathetic nervous system
– Controls vasoconstriction/vasodilation of vessels
• Tunica externa (tunica adventitia)
– Collagen fibers that protect and reinforce vessels
– Larger vessels contain vasa vasorum
General Histology Structure of Blood
Vessels
A Comparison of a Typical Artery and a
Typical Vein
Histological Structure of Blood
Vessels
• Thick-walled arteries near the heart; the aorta and its major branches
– Large lumen (2.5-1 cm diameter) allow low-resistance conduction of blood
and act as conduits
– Contain elastin in all three tunics
– Withstand and smooth out large blood pressure fluctuations
– Allow blood to flow fairly continuously through the body
Elastic (Conducting) Arteries
Large (Elastic) artery.
• Elastic Arteries are classified by:
• The tunica intimae consists of a lining of endothelial cells
that rest on a thin layer of connective tissue.
• The tunica media arranged as lamellae, interspersed with the
smooth muscle cells of the tunica media and collagen fibers
are found between the layers of elastic fibers
• There are no elastic lamellae in the adventitia, but elastic
fibers are present, though relatively few in number and can
not be observed by H&E stain.
• Brown adipose tissue is one of the two types of adipose
tissue. Its primary purpose is to generate body heat. In
contrast to white adipocytes (fat cells) which contain a
single, large fat vacuole, brown adipocytes contain several
smaller vacuoles and centrally located nuclei.
Elastic (Conducting) Arteries
Muscular arteries
• The tunica intimae consists of an endothelial lining and a small
amount of connective tissue.
• The muscular arteries are characterized by a layer of internal
elastic lamina separating the tunica intima from the tunica media.
• The artery has a thicker tunica media, a narrower lumen than the
similarly sized vein, and thickened elastic laminae that are not
present in the vein.
• Muscular arteries have more smooth muscle and less elastin in the
tunica media than elastic arteries.
• The less prominent and more variable external elastic lamina lies
between the tunica media and the adventitia.
• The tunica adventitia is composed of collagen fibers (pink), elastic
fibers (black) and vasa vasorum.
30
Muscular arteries Are called distributing
arteries
– Middle sized
.3mm-1cm
– Changes diameter
to differentially
regulate flow to
organs as needed
– Internal as well as
external elastic
lamina
– Most of what we
see as “arteries”
Tunica media larger in proportion to the
lumen, thus “muscular”
Muscular artery
This slide is stained with Verhoeff's stain to visualize the elastic fibers, and with eosin to
show the cellular structures.
36
Tunica media has only a few layers of
smooth muscle cells
Arterioles – Smallest: .3mm-
10um
– Only larger ones have all 3 layers
– Regulated 2 ways:
• Locally in the tissues
• Sympathetic control
– Systemic blood pressure can be regulated through them
– Deliver blood into capillaries
• Arterioles – smallest arteries; lead to capillary beds
– Control flow into capillary beds via vasodilation and
constriction
“muscular” middle sized artery
Endothelial
cell
Smallest ARTERIOLE
Smallest arteriole, in essence, is a capillary with smooth muscle
cells wrapped around it, with modifications to the endothelial
cells - less transport, more interaction with SMCs.
Smooth muscle
cell SMC/
VSMC Reticular fibers
Contraction regulates flow
by need Vasoconstriction
For fast flow &
non-stick, until
clotting is needed
Controls passage
through the wall
Helps control
blood flow
Mechanical support
Capillaries
Heart to arteries to capillaries to veins to heart
• Capillaries are smallest – 8-10um
– Just big enough for single file erythrocytes
– Composed of: single layer of endothelial cells surrounded by basement membrane
• Universal function – Oxygen and nutrient delivery to tissues
– CO2 and nitrogenous waste (protein break-down product) removal
• Some also have tissue specific functions
The Organization of a Capillary Bed
Capillary Beds
• A microcirculation of interwoven networks of
capillaries, consisting of:
– Vascular shunts – metarteriole–thoroughfare
channel connecting an arteriole directly with a
postcapillary venule
– True capillaries – 10 to 100 per capillary bed,
capillaries branch off the metarteriole and return
to the thoroughfare channel at the distal end of the
bed
44
Capillary Structure
Figure 21.4
Continuous Capillaries
• Continuous capillaries are
abundant in the skin and muscles,
and have:
– Endothelial cells that provide
an uninterrupted lining
– Adjacent cells that are held
together with tight junctions
– Intercellular clefts of unjoined
membranes that allow the
passage of fluids
• Continuous capillaries of the
brain:
– Have tight junctions
completely around the
endothelium
– Constitute the blood-brain
barrier
Fenestrated Capillaries
• Found wherever
active capillary
absorption or filtrate
formation occurs
(e.g., small intestines,
endocrine glands,
and kidneys)
• Characterized by:
– An endothelium
riddled with pores
(fenestrations)
– Greater
permeability to
solutes and fluids
than other
capillaries
Sinusoids • Highly modified, leaky,
fenestrated capillaries
with large lumens
• Found in the liver, bone
marrow, lymphoid
tissue, and in some
endocrine organs
• Allow large molecules
(proteins and blood
cells) to pass between
the blood and
surrounding tissues
• Blood flows sluggishly,
allowing for modification
in various ways
• Collect blood from all tissues and organs
and return it to the heart
• Are classified according to size
– Venules
– Medium-sized veins
– Large veins
Veins
The transition from capillaries to venules
occurs gradually
• The immediate postcapillary venules are similar structurally
to capillaries, with pericytes, but range in diameter from 15 to
20 m.
• A. Postcapillary venules participate in the exchanges between
the blood and the tissues and, are the primary site at which
white blood cells leave the circulation at sites of infection or
tissue damage.
• B. Venules converge into larger collecting venules which have
more contractile cells. With greater size the venules become
surrounded by recognizable tunica media with two or three
smooth muscle layers and are called C. Muscular venules.
• A characteristic feature of all venules is the large diameter of
the lumen compared to the overall thinness of the wall
• Venules collect blood from capillary networks
and gradually merge to form veins. Venules
PCV: Postcapillary venules. CV: Capillary
venules. MV Musculsr venules
Veins
• Blood entering veins is under very low pressure and moves
toward the heart by contraction of the tunica media and external
compressions from surrounding muscles and other organs.
Valves project from the tunica intima to prevent back-flow of
blood.
• Most veins are small or medium veins with diameters less than
one centimeter.
• Located in parallel with corresponding muscular arteries.
• The intima usually has a thin subendothelial layer
• The media consists of small bundles of smooth muscle cells
intermixed with reticular fibers and a delicate network of elastic
fibers.
• The collagenous adventitial layer is well-developed.
Small Veins.
• (a): Micrograph of small vein (V) shows a relatively large
lumen compared to the small muscular artery (A) with its
thick media (M) and adventitia (Ad). The wall of a small vein
is very thin, containing only two or three layers of smooth
muscle. X200. H&E.
Medium sized vines • Vein with a much less
compact muscle layer than you saw in the preceding arteries. unica media and adventitia, which is at least as wide as the media, and often even wider.
• There is no evident inner elastic membrane
• (b): Micrograph of a convergence between two small veins showing valves (arrow). Valves are thin folds of tunica intima projecting well into the lumen which act to prevent backflow of blood. X200. H&E.
(c): Micrograph of a
medium vein (MV)
showing a thicker
wall, but still less
prominent than that
of the accompanying
muscular artery
(MA). Both the
media and
adventitia are better
developed, but the
wall is often folded
around the
relatively large
lumen. X100. H&E.
• (d): Micrograp
h of a medium
vein containing
blood and
showing valve
folds (arrows).
X200. Masson
trichrome.
{ Adventitia
{
Intima
Bundles of longitudinal smooth muscle
Occasional circular SMC Numerous elastic fibers
LARGE VEIN Details
• The big venous
trunks,
Paired with elastic arteries close to
the heart, are large veins
Large veins have a well-developed
tunica intima, but the tunica
media is relatively thin, with
few layers of smooth muscle and
abundant connective tissue. The
adventitial layer is thick in large
veins and frequently contains
longitudinal bundles of smooth
muscle. Both the media and
adventitia contain elastic fibers,
but elastic laminae like those of
arteries are not present.
• Most veins have valves, but
these are most prominent in
large veins.
Special features of
veins
• veins contain valves
– Prevent backflow of blood
• Valves
– Prevent backflow
– Most abundant in legs (where
blood has to travel against
gravity)
• Muscular contraction
– Aids the return of blood to heart
in conjunction with valves
Mechanical issues…
(really good to know)
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